Compound reed oscillator or filter

ABSTRACT

An electromechanical oscillator or filter made up of one, or a pair of, primary reeds supported at one end for mechanical oscillation, each primary reed being slotted so as to form a secondary reed lying in the plane of the primary reed and having its free end adjacent the supported end of the primary reed. A pair of reeds may be constituted by the tines of a tuning fork. Each secondary reed is associated with a magnet and coil to enable mechanical oscillation to be maintained by a conventional electrical maintaining circuit. The secondary reeds may have magnetic members which cooperate with a wavy magnetic track on a driving wheel to provide a rotary drive.

United States Patent [72] Inventor Cecil Frank Clifford Newbridge Works, Bath, Somerset, England a [21] Appl. No. 831,189 [22] Filed June6, 1969 [45] Patented July 6, 1971 [54] COMPOUND REED OSCILLATOR 0R FILTER 9 Claims, 6 Drawing Figs.

3,024,429 3/1962 Cavalieri etal Primary ExaminerMilton 0. i-iirshfield Assistant ExaminerB. A. Reynolds AttorneysEmory L. Groff and Emory L. Groff, Jr.

ABSTRACT: An electromechanical oscillator or filter made up of one, or a pair of, primary reeds supported at one end for mechanical oscillation, each primary reed being slotted so as to form a secondary reed lying in the plane of the primary reed and having its free end adjacent the supported end of the primary reed. A pair of reeds may be constituted by the tines of a tuning fork. Each secondary reed is associated with a magnet and coil to enable mechanical oscillation to be maintained by a conventional electrical maintaining circuit. The secondary reeds may have magnetic members which cooperate with a wavy magnetic track on a driving wheel to provide a rotary drive.

PATENTEUJUL 6|97l Q 3591814 sum 2 UF 3 COMPOUND REED OSCILLATOR R FILTER This invention relates to electromechanical apparatus which may be used as an oscillator or filter.

In known electromechanical oscillators the mechanical oscillating member is often a single reed or a pair of reeds constituted by the tines of a tuning fork. Such devices may be used as filters, or to obtain an alternating current of a particular frequency corresponding to the reed or fork frequency, and in many cases a rotary output is required to drive the mechanism of a clock or other timing device. The reed or reeds islare kept oscillating by means of an' electrical maintaining circuit usually powered by a small battery.

In the known arrangements the oscillating reed is supported at one end while the tines of the fork are integral with the curved center portion which constitutes the support point. The reed or the tines of the fork have magnets or coils attached to them and they swing to and fro in arcs. This generates a centrifugal force and certain inertial forces at each swing which produce undesired reactions on the support tending to produce noise and vibration, apart from other undesirable effects. Moreover the arcuate movement of the or each magnet or coil with respect to the stationary cooperating member produces a position error. Where a rotary drive is required and this is achieved by the use of an escape wheel of known kind having a wavy magnetic track, the arcuate movement is disadvantageous. The principal object of the invention is to provide an electromechanical apparatus for use as an oscillator or filter incorporating an improved form of oscillating member or reed which may be used singly or in pairs, or may be constituted by the tines of a tuning fork. The improved reed is slotted in such a way as to form a secondary reed lying in the plane of the primary reed with the free end of the secondary reed adjacent the supported end of the primary reed. The invention consists of an electromechanical apparatus comprising at least one flexible primary reed supported at one end to permit mechanical oscillation, the primary reed being slotted in such a manner as to form a secondary reed lying in the plane of the primary reed and having its free end adjacent the supported end of the primary reed, and a coil and a magnetic element associated with the secondary reed for maintaining mechanical oscillation of the primary and secondary reed by means of an electrical maintaining circuit.

Where a rotary output is required a magnetic member may be attached to the secondary reed adjacent its free end to cooperate with a wavy or undulating magnetic track on a driving wheel ofa kind in itself known.

The apparatus may comprise a pair of reeds mounted on a common supporting structure, there being a magnetic element and a coil associated with each secondary reed for maintaining mechanical oscillation. The two reeds of the pair may be constituted by the tines ofa tuning fork. Where a pair of reeds or a tuning fork is used either one or both of the secondary reeds may have a magnetic member to provide a magnetic drive to a driving wheel.

In one form of the invention a magnetic element is attached to the free end of the or each secondary reed for mechanical oscillationtherewith, there being a fixed coil associated with each magnetic element for connection to the maintaining circuit.

In'another form ofthe invention in which a pair of reeds or a tuning fork is used there may be either one or two coils lying between the two secondary reeds or the tines and one or both of the coils may have a permanent magnet as a core.

Selected embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a perspective drawing of an electromechanical apparatus according to the invention embodying a pair of primary reeds;

FIG. 2 is a perspective drawing of an electromechanical apparatus according to the invention embodying a tuning fork in which secondary reeds are formed in the tines;

FIG. 3 shows a strip of metal punched with slots from which a tuning fork may be formed;

FIG. 4 shows the strip of FIG. 3 bent to the shape ofa tuning fork;

FIG. 5 shows an embodiment of the invention employing a tuning fork with a pair of coils lying between the tines of the fork; and- FIG. 6 shows a part of a known type of magnetic escape wheel which may be used as a driving wheel'in the embodiment of FIGS and in other embodiments of the invention.

Referring to FIG. 1, one form of apparatus according to the invention comprises a pair of primary reeds l1 and 12. The read I I is supported at one end 13 and is formed near this end with a central slot or opening 14 from which two narrow longitudinal .slots 15 and 16 extend to a point near the unsupported end 17. The slots form a secondary reed I8 which lies within the plane of the primary reed II. The primary reed 12 is identical, being supported at one end 19 and formed with openings or slots 20, 21 and 22 extending to a point near the unsupported end 23 to form a secondary reed'24.

The supported ends 13 and 19 of the reeds 11 and 12 are clamped between a central brass block 25 and two end blocks, respectively 26 and 27, made from a synthetic plastics insulating material, the end blocks being attached to the central block by screws 28 and 29 and two further screws not shown.

Attached to the unsupported end of the secondary reed 18 is a magnetic element 30 which may be a small permanent magnet. A similar magnetic element 31 is attached to the free end of the secondary reed 24. The insulating end block 26 contains a bore 32 into which a coil (not seen) is fitted. The coil may be wound on a circular bobbin or former and impregnated with a medium which hardens so that the coil is selfsupporting in the bore 32. A part of the magnetic element 30 which projects from the unseen side of the secondary reed 18 moves within the tunnel when the reed I8 oscillates so that the coil is inductively coupled to the magnetic element 30.

Following the same construction, a magnetic element 31 is attached to the free end of the secondary reed 24 and a coil 34 is fitted in a bore 33 in insulating block 27 so that the coil 34 is inductively coupled to the magnetic element 31. The coil 34 and the companion coil are for connection to a maintaining circuit which may be a single amplifying transistor contained in a cavity (not seen) in the central block 25. An insulating member 35 attached to the central block 25 has several insulated electrical connection points so that the transistor and the whole of the associated circuitry including a resistor 36 is carried by the block and the member 35, a pair of leads 37 providing a connection to a small dry" cell or its equivalent. The coils are connected respectively to the input and output ends of the maintaining circuit so that as the reeds oscillate small signals are induced in the one coil (the signal coil) and applied to the maintaining circuit while corresponding amplified impulses derived from the maintaining circuit are applied to the other coil (the drive coil) to maintain the reeds in oscillation.

In operation, oscillation of the reeds is maintained by the maintaining circuit, the frequency of oscillation being determined by the natural frequencies of the two reeds which are, of course, identical. Since the secondary reeds are placed the opposite way round with respect to the primary reeds the centrifugal and inertial forces produced by the secondary reeds act against those produced by the primary reeds so that the reaction on the support is the difference between the two sets of forces and is very much smaller. The total effect of these features is that the oscillator functions in a much more precise and reliable manner than known oscillators.

As so far described the apparatus of FIG. I may be used as a frequency standard by taking the signals from one of the coils and employing them to produce an alternating current or a train of impulses having a frequency equal to the reed frequency.

Where a rotary output is desired it may be obtained quite easily, and a favored form of rotary drive which is illustrated consists of an escape wheel, 38 formed with a wavy magnetic track 39, which is in itself known. The escape wheel is mounted on a spindle 40 carried in a bearing 41 provided in the central block 25 in another bearing which is not seen. A magnetic member in the form of a pin 42 made of a magnetic material is attached to the magnetic element 30 and a similar pin 43 is attached to the magnetic element 31. As the secondary reeds oscillate the pins 42 and 43 cooperate magnetically with the wavy track to rotate the escape wheel 38. The combination of the primary and secondary reeds according to the invention produces an almost rectilinear oscillating movement of the magnetic elements. A more precise and uniform drive of the escape wheel is thus provided than if the magnetic elements were to swing in an arc, as in the case of known devices. The pins 42 and 43 could be omitted and the magnetic elements 30 and 31 could be shaped to cooperate directly with the wavy magnetic track.

The embodiment illustrated in FIG. 1 contains a pair of primary reeds 11 and 12 each slotted to form a secondary reed. It will be evident that the oscillator would function with only one primary and secondary reed. In that construction the two coils would take the form of a single coil with atapping, the single coil cooperating with the magnetic element on the one secondary reed.

An electromechanical oscillator in which one or more oscillating elements cooperate with a wavy magnetic track formed on one face only of an escape wheel is disclosed in our British Pat. No. 1,128,394. Another electromechanical oscillator in which one magnetic element cooperates simultaneously with a coil to produce input signals for a maintaining circuit and with a wavy magnetic track on an escape wheel to drive the wheel is disclosed in our British Pat. No. 1,137,850.

In the embodiment of the invention shown in FIG. 1 two separate reeds are employed. The advantages of the invention may also be obtained with a tuning fork, the tines of which are formed to provide the secondary reeds, and this is shown in FIG. 2, only the essential elements being included in the drawing. In FIG. 2 the tuning fork is generally indicated by reference 45 and it is made by bending a strip of suitable material into the shape of a U to form two tines, respectively 46 and 47, joined by a curved portion 48. Each of the tines constitutes a primary reed and is provided with a central slot or opening and two longitudinal slots, as described in relation to the separatereeds of FIG. 1, to form two secondary reeds 49 and 50. A central block 51 forms a support to which the fork is attached at the center of the U portion. The central block 51 contains a bearing 52 for a spindle 53 on which an escape wheel 54 having a wavy magnetic track is mounted.

Two side blocks 55 and 56, preferably made of an insulating material, are provided and these have bores, respectively 57 and 58 which contain a signal coil and a drive coil. The secondary reed 49 carries a magnetic element 59 which is inductively coupled to the coil in the side block 55 and is provided with a magnetic member constituted by a pin 60 which cooperates with the wavy magnetic track of the escape wheel 54 to provide the rotary drive. The secondary reed 50 carries a magnetic element 61 which is inductively coupled to the coil contained in the side block 56 and is provided with a magnetic pin 62 which cooperates with the wavy magnetic track of the escape wheel.

FIG. 3 shows a strip 63 of metal, rectangular in fonn, which may conveniently be made from an alloy having a zero temperature coefficient of elasticity, such as the nickel-iron alloy known as NiSpan C. This strip is formed with two U-shaped slots, respectively 64 and 65, by punching out the material from the slots, to leave two tongues, respectively 66 and 67 which constitute secondary reeds. The strip as a whole is then bent to the U form ofa tuning fork as shown in FIG. 4, leaving the ends of the secondary reeds 66 and 67 projecting at the curved portion of the fork. This is a very convenient method of manufacture since by its use the improved tuning fork according to the invention can be produced very economically.

In the embodiment of FIG. 5 there is shown a tuning fork 68 consisting of two tines 69 and 70 and a curved portion 71 attached, at its center, to a support 72 which carries the fork. The two tines 69 and 70 form primary reeds in which secondary reeds, respectively 73 and 74, are formed in the manner already described in connection with FIGS. 3 and 4. The secondary reed 73 has a magnetic member 75 attached to it at its end and this member is in the form of a permanent magnet. The secondary reed 74 has a member 76 attached to it at its end but, in the present case, it is only a weight to balance the weight of the magnet 75. If it were required to cooperate with the wavy magnetic track of a driving wheel it would also be a magnet. The magnet 75 on the secondary reed 73 cooperates with the wavy magnetic track of a driving wheel, represented by dotted circles 77, which is carried on a spindle supported in pivot bearings, one of which is shown at 78. The driving wheel is of a kind which is well known as a magnetic escape wheel and is illustrated in FIG. 6, to be described.

Between the tines of the fork, and more particularly between the secondary reeds, is a pair of coils 79 and 80 each wound on a bobbin and supported in any convenient manner. Each coil is provided with a core, respectively 81 and 82, and at least one of the cores is a permanent magnet. If only one permanent magnet is used the magnetic circuit is completed 1 through the other core which is of high permeability material,

and if two magnets are used they are preferably so placed that the magnets and the adjacent parts of the secondary reeds form a series magnetic circuit. If desired, the magnets could be so placed that both N poles are adjacent one secondary reed and both S poles are adjacent the other secondary reed.

One end of the coil 79 is connected to the input of an amplifier, shown schematically at 82, which may, and conventionally does, consist of a single transistor powered by a small dry" cell. The other end of the coil 79 and one end of the coil 80 are connected together and, via a lead 83, to the common ground or earth connection of the amplifier. The other end of the coil 80 is connected to the amplifier output. The operation is as described previously in connection with FIG. 1.

FIG. 6 shows a magnetic escape wheel which is in itself known and which may be used as a driving wheel where a rotary output is required. It comprises a spindle 84 carrying a hub 85 to which a disc 86 is attached, only a part of the disc being shown. The disc is formed with rounded slots around its periphery to leave radial teeth 87. The disc is also formed with shaped apertures 88 defining spokes 89. The rounded bottoms of the slots and the outer parts of the apertures define a wavy magnetic track 90.

The form of driving wheel shown in FIG. 6 may be used in any embodiment of the invention, as may the type of driving wheel shown in FIGS. 1 and 2. A vibration damping flywheel or inertia wheel may be mounted on the same spindle as the 7 driving wheel.

lClaim:

1. An electromechanical apparatus comprising at least one flexible primary reed supported at one end to permit tines oscillation thereof about the said one end, the primary reed being slotted in such a manner as to form an integral flexible secondary reed enclosed by and lying in the plane of the primary reed supported at the free end of the primary reed and having its free end adjacent the supported end of etc., primary reed, said secondary reed constructed to mechanically oscillate, about its support with the free end of said primary reed, an electrical maintaining circuit, and a coil and a magnetic element associated with a region of the secondary reed adjacent its free end for maintaining mechanical oscillation of the primary and secondary reeds by means of the electrical maintaining circuit, the primary and secondary reeds adapted to oscillate at the same frequency, whereby centrifugal and inertial forces produced by the oscillations of the individual reeds about oppositely disposed supports oppose each other and are substantially cancelled out.

2. An apparatus as claimed in claim ll comprising a magnetic member attached to the secondary reed adjacent its free end, and a driving wheel having a wavy magnetic track around at least one face, the magnetic member cooperating with the wavy magnetic track to rotate the driving wheel as the reed oscillates.

3. An apparatus as claimed in claim 1 comprising a pair of reeds mounted on a common supporting tines there being a coil and a magnet associated with the secondary reeds by which mechanical oscillation of the primary and secondary reeds is maintained.

4. An apparatus as claimed in claim 3 in which the pair of reeds is constituted by the times of a tuning fork.

5. An apparatus as claimed in claim 3 comprising a magnetic member attached to one secondary reed, and a driving wheel having a wavy magnetic track, the magnetic member cooperating with the wavy magnetic track to rotate the driving wheel.

6. An apparatus as claimed in claim 3 comprising a magnetic member attached to each secondary reed adjacent its free end, and a driving wheel having a wavy magnetic track, the magnetic members cooperating with the wavy magnetic track to rotate the driving wheel.

7. An apparatus as claimed in claim 3 comprising at least one coil lying between the secondary reeds and inductively coupled to both, and a magnetic core inside the coil.

8. An apparatus as claimed in claim 3 comprising a pair of coils between the secondary reeds and inductively coupled to both, and a magnetic core inside each coil, at least one core being a permanent magnet.

9. An apparatus as claimed in claim comprising a magnet attached to the secondary reed adjacent its free end for mechanical oscillationtherewith, there being a fixed coil associated with the magnet for connection to the maintaining circuit.

( A 7 r o v CERTHICATEL ii CQLLKLL- LON Patent No. 3,591,814 D d July 6, 1971 Inventor) CECIL FRANK CLIFFORD It is certified that error appears in the above-idantified patent and that said Letters Patent are hereby correctod as shown below:

Claim 9, line 1, after "claim" insert -3--.

Signed and sealad this 2nd day of November 1971.

(SEAL) Attest:

TCHER JR. ROBERT GOTTSCHAL fi g ifig ficer Acting Commissioner of Patents 

1. An electromechanical apparatus comprising at least one flexible primary reed supported at one end to permit tines oscillation thereof about the said one end, the primary reed being slotted in such a manner as to form an integral flexible secondary reed enclosed by and lying in the plane of the primary reed supported at the free end of the primary reed and having its free end adjacent the supported end of etc., primary reed, said secondary reed constructed to mechanically oscillate, about its support with the free end of said primary reed, an electrical maintaining circuit, and a coil and a magnetic element associated with a region of the secondary reed adjacent its free end for maintaining mechanical oscillation of the primary and secondary reeds by means of the electrical maintaining circuit, the primary and secondary reeds adapted to oscillate at the same frequency, whereby centrifugal and inertial forces produced by the oscillations of the individual reeds about oppositely disposed supports oppose each other and are substantially cancelled out.
 2. An apparatus as claimed in claim 1 comprising a magnetic member attached to the secondary reed adjacent its free end, and a driving wheel having a wavy magnetic track around at least one face, the magnetic member cooperating with the wavy magnetic track to rotate the driving wheel as the reed oscillates.
 3. An apparatus as claimed in claim 1 comprising a pair of reeds mounted on a common supporting tines there being a coil and a magnet associated with the secondary reeds by which mechanical oscillation of the primary and secondary reeds is maintained.
 4. An apparatus as claimed in claim 3 in which the pair of reeds is constituted by the times of a tuning fork.
 5. An apparatus as claimed in claim 3 comprising a magnetic member attached to one secondary reed, and a driving wheel having a wavy magnetic track, the magnetic member cooperating with the wavy magnetic track to rotate the driving wheel.
 6. An apparatus as claimed in claim 3 comprising a magnetic member attached to each secondary reed adjacent its free end, and a driving wheel having a wavy magnetic track, the magnetic members cooperating with the wavy magnetic track to rotate the driving wheel.
 7. An apparatus as claimed in claim 3 comprising at least one coil lying between the secondary reeds and inductively coupled to both, and a magnetic core inside the coil.
 8. An apparatus as claimed in claim 3 comprising a pair of coils between the secondary reeds and inductively coupled to both, and a magnetic core inside each coil, at least one core being a permanent magnet.
 9. An apparatus as claimed in claim comprising a magnet attached to the secondary reed adjacent its free end for mechanical oscillation therewith, there being a fixed coil associated with the magneT for connection to the maintaining circuit. 